...so I've only used it on maybe a hundred shots so far and I'm still perfecting it.

The idea behind it is to digitally recreate the background as it already exists. You may have seen a photo in which the background was changed or replaced and the lighting on the subject doesn't work with the new background at all. The light source(s) may be coming from a different angle or look too hard or too soft, or are the wrong tone or color. When I recreate my backgrounds, they're always almost exactly the same as they were in the original photo, so that the lighting dynamics are the exact same as well. Color can be added as long as the value remains the same as, or similar to, the original background. Exceptions can be made for any of these rules, but only in certain conditions.

The hair and shadows on the ground are the trickiest parts. In a few of the first photos on which I was using this technique, the shadows were 100% photoshop, like this...